Study on a luminol-based electrochemiluminescent sensor for label-free DNA sensing.

Automatic, inexpensive, simple and sensitive methods for DNA sensing and quantification are highly desirable for biomedical research. The rapid development of both the fundamentals and applications of electrochemiluminescence (ECL) over the past years has demonstrated its potential for analytical and bio-analytical chemistry. This paper reports the quenching effect of DNA on the ECL of luminol and the further development of a DNA sensing device. With the pre-functionalization by a composite of carbon nano-tubes (CNTs) and Au nanoparticles (AuNPs), the sensor provides a novel and valuable label-free approach for DNA sensing. Here the ECL intensity was remarkably decreased when more than 1.0 × 10(-12) molar of DNA were adsorbed on the sensor. Linearity of the DNA amount with the reciprocal of ECL intensity was observed. A saturated sensor caused a 92.8% quenching effect. The research also proposes the mechanism for the quenching effect which could be attributed to the interaction between luminol and DNA and the elimination of reactive oxygen species (ROSs) by DNA.

[Spectrophotometric determination of deoxyribonucleic acid by its quenching effect on acridine orange].

Based on the reaction of acridine orange with deoxyribonucleic acid (DNA), and under the optimized condition, a novel method to determine the DNA was developed with the spectrophotometry. The absorbance of acridine orange at the maximum absorption wavelength of 444 nm responded to the concentration of DNA negatively with excellent linearity. It has an upper linear limit concentration of 8.0 microg x mL(-1) and a detection limit of 0.12 microg x mL(-1) with the correlation coefficient of 0.999 8. The method is simple, rapid and sensitive, and could be applied to sample assay satisfactorily. Finally, the reaction mechanism is discussed.

[Studies on sensitization for electrochemiluminescence of luminol with platinum-gold bimetallic nanoparticles modified electrode].

The present paper reports the researches on sensitization of nano-bimetalic material for the electrochemiluminescence (ECL) of luminol. The platinum-gold bimetallic nanoparticles with different component ratio and size were prepared by chemical reduction. The analytical methods such as UV-Vis spectra, TEM and XRD were applied to characterize the properties ofthe nanoparticles. The information obtained from these methods revealed that the prepared bimetallic nanoparticles were truly of alloy structure and absolutely not the mixture of two kinds of metallic nanoparticles. The components of the nanoparticles could be regulated for a series of Pt/Au ratios and the diameters determined by laser-granulometer. In alkaline medium of pH 12.0, the bimetallic Pt-Au nanoparticle modified electrode sensitized the electrochemiluminescence of luminol. The sensitization efficiency reached as high as one order of magnitude with the 6:1 of Pt/Au ratio. The specific surface area of nanoparticles would be larger as the size diminishes, resulting in a higher surface activity, so the smallest size of nanoparticles led to the highest efficiency.

Titania nanotubes decorated with gold nanoparticles for electrochemiluminescent biosensing of glycosylated hemoglobin.

A glycated hemoglobin (HbA1c) biosensor with high performance has been constructed in this work. Here the fructosyl amino acid oxidase was immobilized onto a pre-functionalized indium tin oxide glass with titania nanotubes decorated with gold nanoparticles. The property of nanocomposite was characterized by transmission electromicroscopy, scanning electron microscopy, electrochemistry and spectroscopy. Under the optimum conditions, fructosyl valine was detected by this biosensor. It exhibited a linear detection range from 4.0 × 10(-9) M to 7.2 × 10(-7) M, and a limit of detection for 3.8 × 10(-9) M at the signal-to-noise ratio of 3. Thus the HbA1c level in whole blood samples of healthy individuals or diabetic patients were evaluated with designed biosensor after pre-treatment of hydrolysis. The results of our detection were closely consistent with that of the standard method. At the same time, our biosensor has some advantages including high sensitivity, disposable usage and low cost, which implies its great promising application in point-of-care testing of HbA1c.

[The determination of glutathione by electrochemiluminescence quenching method].

Glutathione is an important active substance in organisms. Its study and determination are very significant to human being's health and life. In neutral medium, the quenching effect of reduced glutathione on the electrochemiluminescence of luminol-iodide was studied in this paper. Therefore a novel sensitive method for the determination of reduced glutathione was developed based on it. The linear response range of this method is from 3.38 x 10(-13) mol x L(-1) to 4.72 x 10(-3) mol x L(-1). This method is the most sensitive one and its linear range is the widest among those reported in the literature.

[Determination of total effective value of flavonoids in propolis by quenched electrochemiluminescence analysis].

Propolis is a kind of quality health foodstuff containing flavonoids, which is an important clinical effective component in many Chinese traditional medicines. The flavonoids could be used to reduce or clear free radicals, which manifests its medical functions. But there are no satisfactory methods to analyze the content of flavonoids in propolis. This paper reports a new method to determine the total effective value of flavonoids in propolis based on quenched effect for iodide-catalyzed electrochemiluminescence of luminol. It is a sensitive and simple method and might be a probable approach to examining the quality of propolis products.

[Determination of I- by the ECL of luminol in neutral medium].

Based on the studies of electrochemiluminescence(ECL) of luminol in neutral medium, the iodide would greatly sensitize the ECL of luminol. The ECL luminous intensity responded linearly to the concentration of iodide within the range of 3.8 x 10(-7) mol x L(-1) to 2.2 x 10(-6) mol x L(-1), and the detection limit is 4.0 x 10(-8) mol x L(-1). The mechanism of enhancement effect of iodide on luminol's ECL is also discussed. The experimental results showed that it was a free radical procedure.

[The study on electrochemiluminescence of luminol on ITO glass].

The indium tin oxide(ITO) glass was applied as the electrode to study the electrochemilumuinescent behavior of luminol on its surface. The experimental results indicated that it was an excellent electrode material for ECL of luminol with very high sensitivity. The detection limit of the luminol is as low as 10(-15) mol x L(-1) order of magnitude. Compared with the voltammetric behavior of luminol, it was revealed that both the two oxidation processes of luminol led to the emission of ECL on the surface of ITO glass,which was different from the ECL behavior of luminol on platinum electrode. Although the ECL intensity of first step oxidation of luminol was relative weak than that of the second step oxidation, it was profitable because it was a reversible process and more stable. It might be useful to fabricate the flow-cell of ECL based on its ECL activity and transparence for light. The influences of the electric parameters and the dissolved oxygen on luminol's ECL on the ITO glass, and the mechanism were also studied in the present paper.

A nano-molar sensitive disposable biosensor for determination of dopamine.

The studies on a nano-molar sensitive disposable biosensor based on the screen-printing basal electrode and the supramolecular assembly of dual mediators, tetramethylbenzidine and ferrocene, by beta-cyclodextrin inclusion complexation have been reported in this paper. This biosensor shows the high quality of analytical performance because of the complexation and the microenvironment in the supramolecular structure. The extracted protein of mushroom, which contains abundant polyphenol oxidase, was immobilized in the membrane of cross-linked cyclodextrin film. This biosensor responds to dopamine with high selectivity and sensitivity. Its response range on the concentration of dopamine is from 1.0 x 10(-9) to 1.0 x 10(-6) M with the detection limit as low as 5.0 x 10(-10) M. The response time reaching to 90% of its steady value is less than 60 s. The biosensor can keep its activity for at least 15 days.

[UV-vis spectroscopic study of the effect of Cu(II) ions on dopachrome].

The effect of Cu(II) ions on dopachrome has been studied by means of UV-Vis spectra in buffer solution at pH 6.5. Cu(II) ions markedly accelerated the rate of bleaching of dopachrome (DC) at 475 nm and simultaneously exhibited general absorption in the range of 300-800 nm in the system with oxygen removed by bubble nitrogen gas. The experimental results revealed that Cu(II) ions catalyzed not only the rearrangement of DC to yield mainly 5 ,6-dihydroxyindole-2-carboxylic acid (DHICA) on first-order kinetics with respect to DC in the first part of the reaction, but also the reaction of 5,6-dihydroxyindole (DHI) and DHICA to form indole-5, 6-quinone (IQ) and indole-5,6-quinone-2-carboxylic acid (IQCA), which would immediately polymerize to yield melanin.

[Spectrophotometric determination of vanadium(V) through the formation of a tungstovanadophosphate-TMBPS charge transfer complex].

A new spectrophotometric method was developed for the determination of vanadium(V). The method was based on the formation of tungstovanadophosphate-3,3',5,5'-tetramethylbenzidine-N-propanesulfonic (TMBPS) charge transfer complex. The spectrophotometric measurements were directly carried out at 450 nm and the apparent molar absorptivity was 2.74 x 10(4) L.mol-1cm-1. The linear range of the determination was 0.02-1 microgram.mL-1. The sensitivity was enhancement with a flotation-extraction preconcentration method and the apparent molar absorptivity was 3.10 x 10(5) L.mol-1cm-1.